Royalty-free products may be used by you multiple times for multiple projects without incurring additional fees. You don't have to pay any additional royalties for successive uses of a royalty-free product. However, as with all Flame Hot Stock licenses, the rights granted are non-transferable and are personal to you. This means that if you license a royalty-free product to be used in a derivative work by your client or any other person, they may not use the licensed product separately from the derivative work.
Royalty-free licenses are always non-exclusive. The product / song / musical piece may be used for any production but may not be altered, performed or distributed outside the scope of your product. In other words you are only allowed to use the music on flame hot stock for your productions but you may not take credit for the work or resell or perform the songs in any way.